Typically, a disk drive system includes a stack of magnetic data storage disks having concentric tracks capable of storing data. A number of read/write transducers or heads, located on actuator arms, are used to communicate with each magnetic data storage disk. The magnetic disks are spun at a high rotational speed causing the transducers to float above the disks on a small cushion of air.
Digital data is written on a disk in the form of magnetic polarity transitions which are induced on the surface of the magnetic disk by a head. The magnetic polarity transitions are written on the magnetic disk by generating a magnetic flux in the head. The magnetic flux induces a magnetic pattern onto the surface of the disk as the disk spins below the head.
In addition to writing data, the head can also be used to read data that has been written on the disk. Reading is performed by sensing a variable magnetic field created by the magnetic pattern on the disk surface as the disk spins. The variable magnetic field is converted to an analog electrical signal that is indicative of the data stored on the disk. This analog electrical signal is commonly called an analog read signal and normally includes a number of readback pulses that each correspond to a single magnetic transition.
As described above, heads are used to write data to and read data from a magnetic media. Some heads, such as a conventional inductive-type head, are capable of performing both functions using a single read/write element. Other heads, known as dual element heads, use separate read and write elements.
Dual element heads are preferable to single element heads because they allow each element to be separately optimized to perform its respective function. For example, a dual element head can utilize a magnetoresistive (MR) read element to perform the reading function. The MR elements are thin strips of magnetoresistive material that have an electrical resistance characteristic that changes with an applied magnetic field. MR elements are more sensitive to small magnetic fields than conventional inductive elements, and therefore, MR elements are preferred over inductive elements for reading data at high disk recording densities.
In the conventional head configuration, shown in FIG. 1, the head 500 includes an MR element 510 as a read element and an inductive write head 530 as a write element. The MR head 500 further includes write coils 535 and shield elements 540. The MR element 510 of MR head 500 is positioned proximate to the surface of rotating magnetic media 520 and is capable of sensing the variable magnetic polarity transitions 525 stored on the magnetic media 520 as the magnetic media 520 is rotated or moved in the direction of arrow A. In addition, MR element 510 is positioned as close to the magnetic media 520 as possible because the amplitude of the readback signal generally increases the closer the MR element 510 is to the media 520.
While dual MR element heads provide certain advantages over inductive heads, the MR head configuration, shown in FIG. 1, is prone to several problems including the problems of thermal asperities, electrostatic discharge and material corrosion. These problems occur, in part, because the MR element 510 is positioned proximate to the magnetic media 520 (in many cases less than a few microinches away) as will be understood by the description of the problems below.
The problem of thermal asperities is well-known in the art. More specifically, the problem is caused by collisions between the head and foreign particles or other aberrations on the surface of the disk. These foreign particles and aberrations are know as asperities. Collisions between the head and the asperities cause the head to heat up. The increase in temperature resulting from the collisions between the asperities and the head causes an increased resistance in the head. Thus, the resulting readback voltage appears to be greater than the voltage that should be present based upon the data stored on the disk. Often, this additive signal exceeds the amplitude of the readback signal. The additive signal resulting from the increase in temperature of the MR element is known as a thermal asperity.
Thermal asperities can cause unwanted increases in bit error rates. In some cases, the increases in bit error rates are so dramatic that severe data losses can result.
In addition, the configuration shown in FIG. 1 is susceptible to the problem of electrostatic discharge due to the generation of an electrostatic potential directly between the MR element 510 and magnetic media 520. When the potential is discharged, the MR head 500 or the MR element 510 may be damaged or destroyed.
Also, the configuration of FIG. 1 may also suffer from the problem of material corrosion. In this configuration, the MR element 510 is directly exposed to chemicals present in the disk drive and chemicals used in the manufacturing processes. These chemicals can corrode the materials used to fabricate the MR element 510. This corrosion may cause damage to the MR element 510 and may result in an inability to retrieve data stored on magnetic media 520.
In an effort to overcome the aforementioned problems, some manufacturers have decided to use yoked MR head structures (see FIGS. 2 and 3). In yoked structures, the MR element is displaced at a distance from the disk surface, embedded in the yoke, and encapsulated in an insulator. A portion of the yoke is placed proximate to the disk surface to effectively “carry” the magnetic flux emanating from the disk to the MR element that is embedded in the yoke. Thus, although the MR element is displaced from the disk surface, the function of the yoke “virtually” places the MR element at the disk surface.
Accordingly, the configurations shown in FIGS. 2 and 3 solve the aforementioned problems. Specifically, with regard to the problem of thermal asperities, the yoke is positioned such that the MR element is recessed and not positioned proximate to the disk surface. As such, the heat that is generated during a collision with an asperity is effectively dissipated in the yoke such that the MR element does not experience the affects of the thermal asperity. With regard to the problem of electrostatic discharge, the MR element is recessed from the disk surface; therefore, an electrostatic potential cannot be generated between the MR element and the disk surface. As such, the risk of discharge is not present. Finally, with regard to the problem of element material corrosion, since the MR element is sealed in an insulator and positioned away from the disk surface, the MR element is not in contact with chemicals used in the manufacturing process or contaminants found in the disk drive. As such, corrosion of the MR element is inhibited.
More specifically, in FIG. 2, a conventional magnetoresistive (MR) head 10 using a yoked geometry is illustrated. The head 10 is used to read information from and write information to a disk 12. Information is written on the disk 12 in the form of longitudinally-recorded magnetic transition data 14. In the conventional geometry shown in FIG. 2, the head 10 includes an MR element 20, a yoke 22, a coil element 24 and a gap 16.
During a read operation, the gap 16 in the yoke 22 senses longitudinally-recorded magnetic transition data 14 on the disk 12 as the disk 12 is rotated or moved in the direction of arrow A. As the longitudinally-recorded magnetic transition data 14 pass the gap 16, the longitudinally-recorded magnetic transition data 14 create a magnetic flux flow within the yoke 22. To sense the flux flow, the MR element 20 is embedded in the flux flow path of the yoke 22. The magnetic flux flow travels through the MR element 20, and thereby varies the resistance of the MR element 20 creating an analog read signal.
During a write operation, a magnetic flux flow is generated in the yoke 22 by energizing coil element 24. When the coil element 24 is energized, a magnetic field is created at the gap 16 which magnetizes the surface of the disk 12 creating longitudinally-recorded magnetic transition data 14.
In FIG. 3, another conventional yoked-head geometry 80 is shown. The head 80 is used only to read information from a disk 86 (i.e., is a read-only head). Information is written on the disk 86 in the form of longitudinally-recorded magnetic transition data 84. The head 80 includes an MR element 82, a flux yoke 88, a gap 87 and a first pole piece 85. As shown in FIG. 3, the MR element 82 is incorporated into the flux yoke 88.
In disk drive or tape drive applications, the magnetic media or disk 86 is rotated or moved in the direction of arrow A′. Like the configuration in FIG. 2, this movement causes longitudinally-recorded magnetic transition data 84 to pass gap 87 and create a magnetic flux flow within the yoke 88. The magnetic flux flow travels through the yoke 88 to the MR element 82 and varies the resistance of the MR element 82 to create an analog read signal.
As mentioned previously, the configurations shown in FIGS. 2 and 3 have advantages over conventional non-yoked head configurations. For example, recessing the MR element 82 from the surface of disk 86 eliminates the problems of thermal asperities, electrostatic discharge and element material corrosion. The head configurations shown in FIGS. 2 and 3, however, suffer from a different problem. More specifically, the readback signal generated by the conventional yoked-head configurations illustrated in FIGS. 2 and 3 during detection or reading of data is a non-ideal pulse signal, as shown in FIG. 4.
In contrast, in most magnetic recording systems, the readback signal generated during a read operation has an ideal pulse shape known as a Lorentzian shape, as shown in FIG. 5. This shape is ideal because it resembles a pulse signal best suited for detection by state of the art detectors. Once delivered to a detector, the Lorentzian-type pulses are read and converted to digital data.
When non-ideal pulse signals are read by conventional yoked MR heads, electronic signal processing techniques must be used to convert the pulse signals into Lorentzian-shaped pulses when partial response like channels are used. For example, the signal shown in FIG. 4 can be converted to a Lorentzian shape by differentiation. The problem with using electronic signal processing techniques is that the signal noise is increased. Also since additional hardware is required to implement the electronic signal processing, such hardware occupies valuable space within the disk drive unit.
Therefore, a need exists for developing a head configuration which possesses the benefits associated with a yoked configuration but also provides a readback signal having substantially Lorentzian-pulse shape without using electronic signal processing. The present invention is designed to overcome the aforementioned problems and meet the aforementioned, and other, needs.